Filters have already been proposed for insertion in the vascular system in order to stop the emboli.
U.S. Pat. No. 3,540,431 describes an umbrella-shaped intravascular filter which comprises divergent arms ending with a tip, and a cap of filtering medium.
U.S. Pat. No. 3 952 747 describes another type of intravascular filter comprising a plurality of divergent arms, joined together by one of their ends, each one ending into a hook at their free end, said arms further comprising U-loops.
Said filters are inserted inside the vena cava where they are held in position by the tips or hooks in contact with the vein inner wall. They are not, however, safely balanced, and it may happen that, under the effect of the flowing blood or of the movements of the vein, these filters topple and become detached from the vein inner wall, thereafter migrating dangerously through the vein and even reaching up to the right auricle of the heart, where they can cause incurable perforations.
Moreover, such filters are not reliable in that their relatively wide meshes can allow part of the emboli to escape and that their filtering capacity is limited.